Bulletin of the American Physical Society
APS April Meeting 2021
Volume 66, Number 5
Saturday–Tuesday, April 17–20, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session Z17: Astrophysics with Gravitational Waves IILive

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Sponsoring Units: DGRAV Chair: Salvatore Vitale, MIT 
Tuesday, April 20, 2021 3:45PM  3:57PM Live 
Z17.00001: Coalescence of Black Holes with Low Mass Gap Objects in Globular Clusters through BinarySingle Exchanges Ilias Cholis, Konstantinos Kritos We study the merger rates of binary black holes in globular clusters that are among the most dense stellar environments and a natural place for the creation of black hole binaries. To model these systems with all their variations we rely on the observational properties of the known Milky Way globular clusters. We include interactions of black hole binaries with stars, with compact objects of mass between 2.5 and 5 solar masses (low mass gap objects) and with black holes as third bodies. Especially the soft interactions with stars accelerate the evolution of these binaries. We implement a simple model to evaluate the merger rate of black holelow mass gap objects mergers formed in globular clustertype environments. We start with starstar binaries and through successive binarysingle exchanges end creating black hole binaries, black holelow mass gap pairs and double low mass gap binaries. We monitor both the different populations of single compact objects, as well as the different combinations of star/low mass gap/black hole binary populations. We find that under proper conditions that exist in certain globular cluster environments, black holelow mass gap mergers can take place at a rate suggested by the detection of GW190814 observed by LIGO's O3 run. [Preview Abstract] 
Tuesday, April 20, 2021 3:57PM  4:09PM Live 
Z17.00002: Pop III binary black holes detections using the next generation gravitationalwave detectors Ken Ng, Salvatore Vitale, Will Farr, Carl Rodriguez Future gravitationalwave (GW) detector networks will detect binaryblackhole mergers (BBHs) up to redshift of z~20, allowing for a direct measurement of the merger history in the “early” universe. Here we show how GW detections of BBHs made by proposed thirdgeneration detectors can be used to search for the Population III (Pop III) binaries dominating at redshift z~10. To identify these Pop III binaries, we first perform a mock data analysis based on the redshift distribution predicted by cosmological simulation, and infer its characteristic peak using Gaussian process regression. Then, we employ phenomenological models to further extract the branching ratio between the Pop III BBHs and the Pop I/II BBHs, as well as the characteristic shape parameters of the subpopulations. With one month of observations at the predicted rate of ~200 Pop III BBHs per month, parameters describing its volumetric merger rate can be constrained at the O(10%) level. [Preview Abstract] 
Tuesday, April 20, 2021 4:09PM  4:21PM Live 
Z17.00003: Characterizing the Population of Binary Black Holes with Detections of Arbitrary Significance Javier Roulet, Tejaswi Venumadhav, Barak Zackay, Liang Dai, Matias Zaldarriaga, Seth Olsen, Horng Sheng Chia In this talk I will describe a novel framework to characterize the population of binary black holes using detections of arbitrary significance. I will quantify the information gain from the inclusion of marginal events and introduce a theoretical bound on the information content of the astrophysical stochastic background, derived with this framework. I will report constraints on the distributions of merging binary black hole masses, spins and rate derived from detections from the first two LIGOVirgo observing runs, including those identified by our group, and how these get updated with results from the recent third observing run. [Preview Abstract] 
Tuesday, April 20, 2021 4:21PM  4:33PM Live 
Z17.00004: Prospects for measuring offaxis spins of binary black hole sources with A+ Alan Knee, Jess McIver, Miriam Cabero Mueller The mass and spin properties of black hole binaries inferred from their gravitationalwave signatures reveal important clues about how these binaries form. For instance, stellarmass black holes that evolved together from the same binary star will have spins that are preferentially aligned with their orbital angular momentum. Alternatively, if the black holes formed separately from each other and later became gravitationally bound, then there is no such preference for having aligned spins. Furthermore, it is known that the presence of misaligned spins induces a general relativistic precession of the orbital plane, imprinting unique structure onto the gravitationalwave signal. The fidelity with which gravitationalwave detectors can measure offaxis spins, or equivalently, precession, will therefore have important implications for the use of gravitational waves to study binary black hole formation channels. I will summarize a new study that examines how well the A+ detector network will measure offaxis spin components, and report preliminary results comparing spin resolution between the fourth and fifth LIGOVirgo observing runs using simulated detector noise and multiple sets of simulated signals distributed over the massspin parameter space. [Preview Abstract] 
Tuesday, April 20, 2021 4:33PM  4:45PM Not Participating 
Z17.00005: Constraining recoil kicks for LIGOVirgo binary black hole populations Vijay Varma, Maximiliano Isi, Sylvia Biscoveanu, Rory Smith When two black holes merge, loss of linear momentum through gravitational radiation can impart a recoil velocity, or a “kick”, to the final black hole. While previous studies have shown that it is difficult to constrain the kick of individual gravitationalwave events at current detector sensitivities, it may still be possible to extract information about the kicks of the binary population as a whole. In this work, we model the kick for each event as drawn from a common underlying distribution, whose properties we infer from the data. We place constraints on the allowed distributions of kicks, which can be used to predict remnant black hole retention rates, and therefore constrain rates of secondgeneration mergers in different formation environments. [Preview Abstract] 
Tuesday, April 20, 2021 4:45PM  4:57PM Live 
Z17.00006: Distinguishing Black Hole Binary Formation Channels With Eccentricity Measurements and Other New Gravity Wave Probes Nicholas DePorzio, Alexandra Shelest, ZhongZhi Xianyu, Lisa Randall Now that we are in a new era of gravitational wave detection it is worth asking how far we can take these measurements in searching for new physics. But to do so we also want to better understand the signals we do see. One outstanding question is the origin of binary black holes. By studying the effects of binary eccentricity on measurements at current and future gravitational wave detectors, we can shed light on the environment in which the black holes were created. We also argue for other interesting measures of the black hole environment and discuss how future gravity wave experiments could probe dark matter or physics associated with the electroweak scale. [Preview Abstract] 
Tuesday, April 20, 2021 4:57PM  5:09PM Live 
Z17.00007: A generalized precession parameter to interpret gravitationalwave data Matthew Mould, Davide Gerosa, Daria Gangardt, Patricia Schmidt, Geraint Pratten, Lucy Thomas Current gravitationalwave data analysis of merging binary black holes accounts for two precessing spins, allowing inference of the six spin degrees of freedom. Nonetheless, it is convenient to use effective parameters to interpret detections; the effective aligned spin $\chi_{\rm{eff}}$ and precessing spin $\chi_{\rm{p}}$ measure spins parallel and perpendicular to the orbital angular momentum, with measurements away from zero indicating large spins and significant precession, respectively. While $\chi_{\rm{eff}}$ is conserved during an inspiral, $\chi_{\rm{p}}$ is not; furthermore, it employs a singlespin approximation that retains some, but not all, precessiontimescale variations. To rectify this inconsistency we propose twospin definitions that either fully consider or fully average those variations. In addition to the previous domain $\chi_{\rm{p}}\in[0,1]$, our generalized parameter presents an exclusive region $1\leq\chi_{\rm{p}}\leq2$ accessible only to binaries with two precessing spins. For current LIGO/Virgo events, our generalized parameter indicates that, while (i) previous measurement errors on $\chi_{\rm{p}}$ may be underestimated, (ii) the evidence for spin precession may be stronger than suggested previously. [Preview Abstract] 
Tuesday, April 20, 2021 5:09PM  5:21PM Live 
Z17.00008: Gravitational Memory Waveforms in BransDicke Theory Shammi Tahura, David Nichols, Kent Yagi Gravitationalwave (GW) memory effects are lasting changes in the GW strain and its time integrals following bursts of GWs. They are closely related to the symmetries of asymptotically flat spacetimes and their corresponding conserved charges. There are three types of GW memory effects (displacement, spin, and centerofmass) that are related to different conserved charges and have different observable effects. GW memory effects are well studied in general relativity (GR) but have not been explored as carefully in theories beyond GR. One of the simplest modified theories of gravity is BransDicke theory, which includes a massless scalar field nonminimally coupled to gravity. This theory has a scalar breathing polarization of GWs in addition to the tensor GWs in GR, and there can be scalar GW memory effects in addition to the tensor GW memory effects. The scalar memory effects are not related to symmetries or conserved quantities, but the scalar waves (and their memory) do affect the tensor memories. I will present the leading Newtonian corrections to the tensor displacement and spin GW memory effects from nonspinning, quasicircular compact binaries in BransDicke theory. [Preview Abstract] 
Tuesday, April 20, 2021 5:21PM  5:33PM Live 
Z17.00009: Memorylike effects arising from relative velocity and acceleration Alexander Grant, David Nichols The gravitational wave memory effect reflects a permanent change in separation of a pair of initially comoving test particles caused by a burst of gravitational waves. Near null infinity, the contributions to the memory effect split into two categories: linear memory, which appears even in linearized gravity, and nonlinear memory, which arises due to the nonlinear nature of general relativity. Moreover, this nonlinear effect is expected to be the dominant contribution to the memory effect for binary black hole mergers, such as those detected by LIGO and Virgo. In this talk, we discuss how the final separation of test particles depends not only on initial separation (as in the usual memory effect), but also the initial relative velocity and the relative acceleration of the test particles. Each of these contributions provides additional memorylike effects near null infinity, and we show that, like the usual memory effect, a similar linear vs. nonlinear split arises. [Preview Abstract] 
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